1. Field of the Invention
The invention relates to enclosures for pressure relief devices, which are also referred to as directional shields. The enclosures temporarily confine fluids discharged through the pressure relief devices and direct the discharged fluids through a relief duct or other conduit. The invention relates particularly to such enclosures that are mounted on electrical equipment housings to control discharges of hot oil/air and protect the surrounding environment.
2. Background Art
Large pressure relief devices on medium to large power transformers (either nitrogen blanket or conservator style), load tap changers, and other electrical equipment protect the equipment from over-pressure conditions. The pressure relief devices, which are commonly referred to as PRD's, must quickly relieve increased pressure that can accumulate in the housings containing such electrical equipment by allowing large quantities of potentially very hot fluids (oil and gas) to escape from the housings in a short time. The devices must respond before the housings in which the electrical equipment is contained rupture and, in so responding, allow a sufficient amount of fluid to be discharged in a sufficiently short amount of time to prevent damage, all while, preferably, discharging fluid in a manner where it will not cause injury or damage to persons or equipment located close by.
Large quantities of hot oil and gas discharged from the pressure relief devices tend to spray out over wide areas unless confined. Such sprays are dangerous and unsafe for the environment. Accordingly, it is becoming an increasingly common practice to enclose the pressure relief devices for temporarily containing and directing the fluids to where the fluids can be more safely recovered or disposed. Generally, the enclosures fit over the top of the pressure relief devices temporarily trapping the fluid discharges between the enclosures and the electrical equipment housings. Duct work is connected to the enclosures for directing the temporarily trapped fluids beyond the pressure relief devices.
The known enclosures are assembled in place over the top of the pressure relief devices. Even in new applications, the pressure relief devices are first mounted on the electrical equipment housings and the conventional enclosures are assembled around the mounted pressure relief devices. Some disassembly of the pressure relief devices is sometimes required to attach the enclosures to the mounted pressure relief devices. Other requirements include the adaptation of indicator or alarm systems, which further complicates the assembly requirements of the enclosure. A number of examples of conventional enclosure systems for a pressure relief valves are disclosed in my co-assigned U.S. Pat. No. 5,937,893, entitled Shield for Pressure Relief Device, which patent is hereby incorporated by reference.
Although the known enclosure designs for pressure relief devices are effective for containing and directing flows of fluid discharged through the pressure relief devices, the assembly of such enclosures in place over pressure relief devices can be quite time consuming and can involve a number of steps made more difficult by other circumstances and requirements of individual electrical equipment housings. Care must be taken that the assembly is done correctly for each different application to safely accommodate the sudden discharge of large quantities of fluid.